序言

在业务中需要显示一个循环滚动的控件，内容可以循环滚动，可以自动滚动，手指触摸的时候会暂停。 由于目前的方案都是基于ViewPager或者RecycleView的。还需要实现Adapter，需要拦截各种事件。使用成本比较高。于是我就自定义了一个控件实现该功能，

使用

使用起来很简单。把需要显示的控件放置在其中就行。就和普通的HorizontalScrollView用法一样。 不过子控件必须要LoopLinearLayout 

效果

• 1.支持左右循环滚动
• 2.支持自动滚动
• 3.支持点击事件
• 4.触摸暂停
• 5.支持惯性滚动
• 6.一共不到300行代码，逻辑简单易于扩展

原理

通过继承自HorizontalScrollView实现，重新onOverScrolled 和 scrollTo 方法在调用supper方法之前，对是否到达边界进行判断，如果到达就调用LoopLinearLayout.changeItemsToRight() 方法对内容重新摆放。

摆放使用的是 child.layout() 的方法，没有性能问题。摆放完成以后，对scrollX进行重新赋值。

需要注意的是在HorizontalScrollView中有一个负责惯性滚动的OverScroller  但是在调用其fling方法之前会设置maxX这导致无法滚动到控件内容之外。所以使用反射修改了这个类。拦截了fling方法 

而动画的时长设置的是滚动一个LoopScrollView宽度需要的时间。还有就是无限循环的动画需要在 onDetachedFromWindow中移除，避免内存泄漏

源码

LoopLinearLayout

package com.example.myapplication;


import android.content.Context;

import android.util.AttributeSet;

import android.view.View;

import android.view.ViewGroup;

import android.widget.LinearLayout;


import androidx.annotation.Nullable;


import java.util.List;


/**

 * Created by zhuguohui

 * Date: 2021/11/30

 * Time: 10:46

 * Desc:

 */

public class LoopLinearLayout extends LinearLayout {

    public LoopLinearLayout(Context context) {

        this(context, null);

    }


    public LoopLinearLayout(Context context, @Nullable AttributeSet attrs) {

        super(context, attrs);

    }



    public void changeItemsToRight(List<View> moveItems, int offset) {


        int offset2 = 0;

        for (int i = 0; i < getChildCount(); i++) {

            View childAt = getChildAt(i);

            if (!moveItems.contains(childAt)) {

                MarginLayoutParams layoutParams = (MarginLayoutParams) childAt.getLayoutParams();

                offset2 += childAt.getWidth() + layoutParams.leftMargin + layoutParams.rightMargin;

                childAt.layout(childAt.getLeft() - offset, childAt.getTop(), childAt.getRight() - offset, childAt.getBottom());

            }

        }

        for(View view:moveItems){

            view.layout(view.getLeft()+offset2,view.getTop(),view.getRight()+offset2,view.getBottom());

        }

    }

    public void changeItemsToLeft(List<View> moveItems, int offset) {


        int offset2 = 0;

        for (int i = 0; i < getChildCount(); i++) {

            View childAt = getChildAt(i);

            if (!moveItems.contains(childAt)) {

                MarginLayoutParams layoutParams = (MarginLayoutParams) childAt.getLayoutParams();

                offset2 += childAt.getWidth() + layoutParams.leftMargin + layoutParams.rightMargin;

                childAt.layout(childAt.getLeft() + offset, childAt.getTop(), childAt.getRight() + offset, childAt.getBottom());

            }

        }

        for(View view:moveItems){

            view.layout(view.getLeft()-offset2,view.getTop(),view.getRight()-offset2,view.getBottom());

        }

    }



}

LoopScrollView

package com.example.myapplication;


import android.animation.Animator;

import android.animation.AnimatorListenerAdapter;

import android.animation.ValueAnimator;

import android.annotation.SuppressLint;

import android.content.Context;

import android.util.AttributeSet;

import android.view.MotionEvent;

import android.view.View;

import android.view.animation.LinearInterpolator;

import android.widget.HorizontalScrollView;

import android.widget.OverScroller;


import java.lang.reflect.Field;

import java.util.ArrayList;

import java.util.List;


public class LoopScrollView extends HorizontalScrollView {


    private LoopScroller loopScroller;

    private ValueAnimator animator;


    public LoopScrollView(Context context) {

        this(context, null);

    }


    public LoopScrollView(Context context, AttributeSet attrs) {

        super(context, attrs);

        setOverScrollMode(OVER_SCROLL_ALWAYS);

        try {

            @SuppressLint("DiscouragedPrivateApi")

            Field field =HorizontalScrollView.class.getDeclaredField("mScroller");

            field.setAccessible(true);

            loopScroller = new LoopScroller(getContext());

            field.set(this, loopScroller);


        } catch (Exception e) {

            e.printStackTrace();

        }


    }


    @Override

    protected void onLayout(boolean changed, int l, int t, int r, int b) {

        super.onLayout(changed, l, t, r, b);

        if(changed||animator==null){

            buildAnimation();

        }

    }


    private void buildAnimation() {

        if(animator!=null){

            animator.cancel();

            animator=null;

        }

        animator = ValueAnimator.ofInt(getWidth() - getPaddingRight() - getPaddingLeft());

        animator.setDuration(5*1000);

        animator.setRepeatCount(-1);

        animator.setInterpolator(new LinearInterpolator());

        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

            int lastValue;

            @Override

            public void onAnimationUpdate(ValueAnimator animation) {

                int value= (int) animation.getAnimatedValue();

                int scrollByX=value-lastValue;

          //      Log.i("zzz","scroll by x="+scrollByX);

                scrollByX=Math.max(0,scrollByX);

                if(userUp) {

                    scrollBy(scrollByX, 0);

                }

                lastValue=value;

            }

        });

        animator.addListener(new AnimatorListenerAdapter() {

            @Override

            public void onAnimationEnd(Animator animation) {

                super.onAnimationEnd(animation);

            }


            @Override

            public void onAnimationStart(Animator animation) {

                super.onAnimationStart(animation);

            }


        });

        animator.start();

    }


    static   class LoopScroller extends OverScroller{

        public LoopScroller(Context context) {

            super(context);

        }


      @Override

      public void fling(int startX, int startY, int velocityX, int velocityY, int minX, int maxX, int minY, int maxY, int overX, int overY) {

          super.fling(startX, startY, velocityX, velocityY, Integer.MIN_VALUE,Integer.MAX_VALUE, minY, maxY, 0, overY);

      }

  }





    @Override

    protected void onDetachedFromWindow() {

        super.onDetachedFromWindow();

        if(animator!=null){

            animator.cancel();

            animator.removeAllListeners();

            animator = null;

        }

    }


    @Override

    protected void onOverScrolled(int scrollX, int scrollY, boolean clampedX, boolean clampedY) {

        if (userUp) {

            //scroller再滚动

            scrollX=loopScroller.getCurrX();

            int detailX = scrollX - lastScrollX;

            lastScrollX = scrollX;

            if(detailX==0){

                return;

            }

            scrollX = detailX + getScrollX();


        }

        int moveTo = moveItem(scrollX,clampedX);


        super.onOverScrolled(moveTo, scrollY, false, clampedY);

    }


    boolean userUp = true;

    int lastScrollX = 0;


    @Override

    public boolean onTouchEvent(MotionEvent ev) {

        if (ev.getAction() == MotionEvent.ACTION_UP) {

            userUp = true;

            lastScrollX = getScrollX();

        } else {

            userUp = false;

        }

        return super.onTouchEvent(ev);

    }

    @Override

    public void scrollTo(int x, int y) {

        int scrollTo = moveItem(x, false);

        super.scrollTo(scrollTo, y);

    }



    private int moveItem(int scrollX, boolean clampedX) {


        int toScrollX = scrollX;


        if (getChildCount() > 0) {

            if (!canScroll(scrollX,clampedX)) {

                boolean toLeft=scrollX<=0;

                int mWidth=getWidth()-getPaddingLeft()-getPaddingRight();

                //无法向右滚动了，将屏幕外的item，移动到后面

                List<View> needRemoveViewList = new ArrayList<>();

                LoopLinearLayout group = (LoopLinearLayout) getChildAt(0);

                int removeItemsWidth = 0;

                boolean needRemove = false;

                for (int i = group.getChildCount() - 1; i >= 0; i--) {

                    View itemView = group.getChildAt(i);

                    MarginLayoutParams params = (MarginLayoutParams) itemView.getLayoutParams();

                    if(toLeft){

                        int itemLeft = itemView.getLeft() - params.leftMargin;

                        if (itemLeft >= mWidth) {

                            //表示之后的控件都需要移除

                            needRemove = true;

                        }

                    }else{

                        int itemRight = itemView.getRight() + params.rightMargin;

                        if (itemRight <= scrollX) {

                            //表示之后的控件都需要移除

                            needRemove = true;

                        }

                    }


                    if (needRemove) {

                        int itemWidth = itemView.getWidth() + params.rightMargin + params.leftMargin;

                        removeItemsWidth += itemWidth;

                        needRemoveViewList.add(0,itemView);

                    }

                    needRemove=false;

                }

                if(!toLeft){

                    group.changeItemsToRight(needRemoveViewList,removeItemsWidth);

                    toScrollX -=removeItemsWidth;

                }else{

                    group.changeItemsToLeft(needRemoveViewList,removeItemsWidth);

                    toScrollX +=removeItemsWidth;

                }


            }


        }

        return Math.max(0, toScrollX);

    }


    private boolean canScroll(int scrollX, boolean clampedX) {

        if(scrollX<0){

            return false;

        }

        if(scrollX==0&&clampedX){

            //表示向左划不动了

            return  false;

        }

        View child = getChildAt(0);

        if (child != null) {

            int childWidth = child.getWidth();

            return getWidth() + scrollX < childWidth + getPaddingLeft() + getPaddingRight();

        }

        return false;

    }

}

最后所有的功能只依赖上述两个类，关于动画的时长写死在类中的，没有抽成方法。有需要的自己去改吧。